Relation between Mössbauer spectroscopy and geometrical frustration factors in MCr1.9857Fe0.02O4 (M = Co, Zn)

In order to elucidate the role of Cr ions in MCr2O4(M = Co, Zn) exhibiting geometrically frustration and multiferroic property, we have substituted a small amount of Fe ions for Cr sites and investigated the magnetic behavior of Fe ions with Mössbauer spectroscopy. The crystal structure was found to be single‐phase cubic spinel with space group of Fd3m. The lattice constants a0 and the internal structural parameter (x) of the oxygen were determined to be 8.340, 8.331 Å and 0.261 and 0.260, respectively. The Mössbauer absorption spectra at 4.2 K show that the well‐developed two sextets are superposed with small difference of hyperfine fields(Hhf). The hyperfine fields of CoCr1.9857Fe0.02O4 and ZnCr1.9857Fe0.02O4 were determined to be 490 ∼ 480 kOe and 460 ∼ 450 kOe, respectively. Isomer shift values (δ) of the two sextets are found to be 0.33 ∼ 0.35 mm/s relative to those of Fe metal, which are consistent with the high spin Fe3+ charge state. From the results of Mössbauer measurement, it is suggested that Cr3+ ions have two different magnetic sites, and there is a correlation between hyperfine fields and degree of magnetic geometrical frustration. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)